What does Mean Platelet Volume (MPV) indicate in a patient's blood work?

Mean Platelet Volume (MPV): Clinical Significance

Mean Platelet Volume (MPV) is an automated measurement of the average size of platelets in femtoliters (fL), typically ranging from 7.5-11.5 fL, and serves as an important indicator of platelet production, activation state, and underlying hematologic or cardiovascular pathology. 1, 2

What MPV Measures

• MPV quantifies the average volume of circulating platelets, measured by automated hematology analyzers during routine complete blood counts 1, 2
• Platelet size is primarily determined in the bone marrow during megakaryocytopoiesis and does not substantially change once platelets enter circulation 3
• Larger platelets are metabolically and enzymatically more active than smaller platelets, containing more granules, producing more thromboxane A2, and demonstrating greater aggregation potential 3, 4

Clinical Interpretation of MPV Values

Elevated MPV (>11.5 fL)

• High MPV with thrombocytopenia indicates increased platelet destruction (immune thrombocytopenic purpura, drug-induced thrombocytopenia, or other hyperdestructive causes), as the bone marrow compensates by releasing larger, younger platelets 2, 5
• High MPV with normal platelet count suggests heterozygous thalassemia, iron deficiency, or early myeloproliferative disorders 2
• High MPV with thrombocytosis occurs in myeloproliferative disorders, chronic inflammation, iron deficiency, or post-splenectomy states 2
• Elevated MPV independently predicts cardiovascular risk, including myocardial infarction, stroke, and mortality after percutaneous coronary intervention 3, 6

Low MPV (<7.5 fL)

• Low MPV that is inappropriately low for the platelet count indicates bone marrow suppression from sepsis, cytotoxic drugs, aplastic anemia, chronic renal failure, or splenomegaly 2
• Low MPV helps distinguish decreased platelet production (bone marrow failure) from increased destruction (where MPV would be elevated) 5
• An MPV <8.4 fL has 71% specificity for decreased platelet production when evaluating thrombocytopenia 5

Diagnostic Algorithm for Thrombocytopenia

When evaluating a patient with low platelet count:

1. Check MPV immediately - it is available on standard complete blood counts 2, 5
2. If MPV is elevated (>8.4 fL): suspect increased platelet destruction (ITP, drug-induced, hypersplenism, disseminated intravascular coagulation) 2, 5
3. If MPV is low or inappropriately normal: suspect decreased production (chemotherapy, aplastic anemia, bone marrow infiltration, sepsis) 2, 5
4. Always examine the peripheral blood smear - MPV cannot replace direct visualization of platelet morphology, including assessment for giant platelets, platelet clumping, or pseudothrombocytopenia 5

Cardiovascular Risk Assessment

• MPV >8.6 fL is associated with increased mortality in patients undergoing percutaneous coronary intervention (hazard ratio 1.18, p<0.001) 6
• Higher MPV correlates with increased platelet reactivity, shortened bleeding time, and elevated thromboxane B2 levels 3, 4
• MPV is elevated in obesity, diabetes mellitus, metabolic syndrome, and acute coronary syndromes, reflecting enhanced platelet activation 3, 6

Critical Pitfalls to Avoid

• Do not rely on MPV alone - it must be interpreted alongside platelet count and peripheral blood smear examination 5
• MPV is superior to manual megathrombocyte counting (sensitivity 80% at MPV ≥8.4 fL vs. 43% specificity for manual counts) but does not replace morphologic assessment 5
• Temperature and anticoagulant timing affect MPV - samples stored at 4°C show falsely elevated MPV, while prolonged storage at 37°C decreases MPV 4
• Platelet activation during blood collection artificially increases MPV - ensure proper collection technique and timely analysis 4
• Giant platelets approaching red blood cell size are not consistent with ITP and mandate investigation for inherited platelet disorders or myelodysplastic syndromes, regardless of MPV value 7